"The Messenger of Allah (ﷺ) said: 'The Imam is appointed to be followed, so when he says the takbir, say the takbir, and when he recites, be silent, and when he says: "Sami' Allahu liman hamidah (Allah hears those who praise Him)," say: "Allahumma rabbana lakal-hamd (Our Lord, to You be praise)."
Reference: Sunan an-Nasa'i 921 In-book : Book 11, Hadith 46 English translation : Vol. 2, Book 11, Hadith 922
Help us gift a modern, ad-free Islamic application for the Muslim Ummah. Your donation will be recorded as Sadaqah Jariyah in your book of deeds, In Sha Allah.